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September 15, 2012

Bakersfield Night Sky – September 15, 2012
By Nick Strobel

Next Saturday is an important day in astronomy. On September 22nd (at 7:49 AM Pacific Daylight Time to be more precise) marks the beginning of the autumn (fall) season. The autumn season officially starts when the Sun crosses the Celestial Equator going from north to south. The Celestial Equator is the projection of the Earth's equator onto the sky, splitting the sky into a north half and a south half. Because the Earth's axis is tipped by 23.5 degrees with respect to its orbit around the Sun, the Sun appears to move along a great circle path through the zodiac constellations called the ecliptic that is tipped by 23.5 degrees with respect to the Celestial Equator. During the spring and summer seasons, the Sun is north of the Celestial Equator and its light hits our part of the Earth more directly. Also, the Sun is up above the horizon for more than 12 hours. During the autumn (fall) and winter seasons, the Sun is south of the Celestial Equator and its light hits our part of the Earth at a more glancing angle, diluting the Sun's light at our latitude.

The transition from summer to autumn happens then, when the Sun reaches the intersection point of the ecliptic and the Celestial Equator. At this boundary between the seasons, the amount of night ("nox") is equal to the amount of day (so, "equi-nox", or equal night). The Sun also rises due East on the equinox date and sets exactly West. For the rest of the days of autumn, the Sun will set further and further south of West until the date of the winter solstice, when it will start moving northward again. All through the autumn season, the amount of daylight will get shorter and shorter.

Another reason why September 22nd is special is that it is International Observe the Moon Night and the Kern Astronomical Society invites you to come help them celebrate at their monthly public star party at Russon' s Books in the Marketplace. The free star party begins shortly after sunset and goes until about 10 PM. The first star chart below shows the evening sky for the star party. See the KAS website for a map to the location. The Moon will be at First Quarter phase so it will be high up in the southern sky when the Sun is setting. At first quarter the Moon is 90 degrees in angle away from the Sun, so we will see the boundary between night and day going right down the middle of the Moon. Through the KAS telescopes, the craters and mountains at the night/day bounday will be especially dramatic from the longer shadows. Those locations at the night/day boundary will see the Sun just beginning to rise up. The Kern Astronomical Society will also have other special activities going on to celebrate Observe the Moon Night, so come on by!

Whether or not you can make it to the free public star party, try out your hand at figuring out the various types of terrain on the surface (craters, boulders, oddly textured terrain, and other features that decorate the lunar surface) in the photos from the Lunar Reconnaissance Orbiter (LRO). This is the "Moon Mappers" project I mentioned in last month's column. Moon Mappers is a citizen-science project that will help us sift through all of the hundreds of gigabytes returned to us every day by LRO. Analyzing all of those volumes of data will be crucial information for future rover and human missions to the Moon. Go to http://cosmoquest.org/mappers/moon/ to see how you can help.

You won't see the Moon in tonight's sky since it is at New Phase where it is roughly lined up with the Sun (but not precisely enough to make a solar eclipse). Look for the thin crescent Moon to develop this coming week. As shown on the first star chart below, the Moon will be to just the left of orange-red Mars on September 19th—both will fit easily in the same view of your binoculars. Mars continues to pull away from Saturn but Saturn is probably too low in the west in the evening twilight for you to spot now. Mars is also getting hard to see but it should be visible in the west among the stars of Libra. In tonight's and tomorrow's sky, Mars will be right next to the "alpha" star of Libra that has the great name "Zubenelgenubi". Mars and Zubenelgenubi will easily fit within the same field of view of your binoculars and your binoculars will also show that Zubenelgenubi is actually a double star.

On Mars, the Mars Science Laboratory rover "Curiosity" continues its instrument check-out phase. It has now moved over a football field's length since it landed while it has been flexing it arm and testing the instruments at the end of its arm. For the instrument check-out and calibration phase of the mission, the MSL team needed to turn Curiosity to a particular angle in relation to the Sun and be on flat ground. Curiosity is a very complex machine that requires careful calibration and practice of all of its motions and instruments. Curiosity will take a few weeks to drive eastward toward a feature in Gale Crater called "Glenelg". That site will very likely offer the first rocks to be drilled by Curiosity. Powder from the drilling will be collected by Curiosity and carefully analyzed by CheMin in the main body of the rover. CheMin will direct a beam of X-rays as fine as a human hair through the powered material. When the X-ray beam interacts with the rock or soil sample, some of the X-rays will be absorbed by atoms in the sample and re-emitted or fluoresced at energies that are characteristic of the particular atoms present. CheMin will give scientists the mineral clues indicative of a past Martian environment that might have supported life. On another part of Mars, Curiosity's older cousin, Opportunity, continues to explore the 14-mile across crater Endeavour Crater. Opportunity found evidence at Endeavour Crater that the original impact 4 billion years ago, released heated underground water that then deposited zinc in the rock. Sometime after the impact, cool water flowed through the cracks in the ground near the edge of the crater and deposited veins of the mineral gypsum—the strongest evidence for an environment with water in the past.

In the early morning sky Venus and Jupiter continue to dominate. Jupiter will be visible by 11:45 PM rising in the east between the horns of Taurus. Jupiter will have another visitor from Earth arriving on the scene in a few years. The Juno spacecraft is getting set up for a gravity assist from a flyby of Earth on October 9th. The Earth gravity assist will boost Juno's speed by over 16,300 mph, giving it the speed it needs to fly the 1.4 billion-mile path on out to the king of the planets. Juno will arrive at Jupiter on July 4, 2016 and it will circle the planet pole-to-pole, probing the planet's interior to learn about its origin. During its formation, Jupiter sucked up most of the material left over from the Sun's formation. Earth and the other planets are made from the small amounts of the remaining stuff. Juno's chief scientist, Scott Bolton explains that "if we want to learn about the history of the elements that made Earth and life, we need to first understand what happened when Jupiter formed." It's all about putting the pieces together of the Earth's origin and that will help us better understand the origins of other habitable worlds beyond the solar system as well as where to look for them.

Venus will be visible rising in the east after 3:45 AM. Venus is closing in on the bright star Regulus at the end of the sickle part of Leo. Venus will have an extremely close conjunction with Regulus on October 3rd. Venus rises about 3.5 hours before the Sun. It is now in the farther part of its orbit with respect to the Earth's position, so its phase is more than half lit—a gibbous phase with a diameter that will shrink over the coming weeks. See the second star chart below for a view of the early morning pre-dawn sky.

Want to see more of the stars at night and save energy? Shield your lights so that the light only goes down toward the ground. See www.darksky.org for how.
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Nick Strobel
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com

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